Influence of Chain Primary Structure and Topology (Branching) on Crystallization and Thermal Properties: The Case of Polysulfides

Abstract

We have investigated how variations in primary structure (distribution of monomeric units, chain length) and degree of branching affect the crystallization behavior of polysulfides. In particular, we have used copolymers of crystallizable (ethylene sulfide, ES) and noncrystallizable (propylene sulfide, PS) units, prepared via anionic ringopening mechanism. PS units interrupt the crystallization of ES sequences; therefore, strong differences in thermal properties are expected between copolymers with a gradient (single addition of ES/ PS mixtures) or a semirandom structure (sequential additions, which yield a more constant composition along the chain). Additionally, we prepared different chain topologies: linear, 4-and 8-armed stars, and combs with 10, 15, and 20 arms, in a comparison where each arm had a gradient primary structure and degree of polymerization (DP) of 10, 20, and 30. The influence of these variables (topology, number of arms, and DP) on the thermal properties was studied by polarized light optical microscopy (PLOM), standard and advanced DSC techniques (i.e., self-nucleation and successive self-nucleation and annealing (SSA)), and small and wide angle X-ray scattering (WAXS and SAXS). First, we have confirmed the much higher order obtained in gradient polymers, in comparison to the semirandom ones. Second, we have seen that the type of crowding of polymer chains affected the level of order achievable. In star polymers, an increasing number of arms increased topological restrictions, which in turn decreased crystallization and melting temperatures, crystallinity, and lamellar thickness. For combs, which are characterized by a more parallel than convergent crowding of the chains, the increase in arms number did not produce a significant decrease in crystalline order; on the contrary, the higher density of chains caused moderate increases in crystallization and melting temperatures, crystallinity, and lamellar thickness.

Self-Nucleation Effects on Polymer Crystallization

“…The lower the value of Ts, the higher is the Tc upon cooling from the melt, indicating a stronger nucleation effect. This peculiar nucleation effect has been termed in different ways in the literature: crystalline memory 38,39,41,[56][57][58]61,63,[66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] , melt memory 49,52,60,64,[81][82][83][84][85][86][87][88][89][90][91][92][93][94] , in some works both terms are used indistinctly 18,47,48,62,65,[95][96][97][98] and in other cases a mo...…”

Versatile Preparation of Branched Polylactides by Low-Temperature, Organocatalytic Ring-Opening Polymerization in N-Methylpyrrolidone and Their Surface Degradation Behavior

“…For a given macromolecular structure, the slope of a versus graph is inversely related to its persistence length; all polymers produced in this study nicely fit with a single slope (Figure C), suggesting a negligible effect of branching. This is likely due to the long PLA chains (100 monomeric units per arm), which overcome the single branching point; this would not be the case for shorter chains, and indeed, we have recently showed that short-armed stars (polysulfides, 10–30 units per arm) have a larger persistence length than linear analogues …”

“…We then assessed the effect of branching and stereoregularity on hydrodynamic properties, first focusing on the Mark− Houwink parameter a. An a value of 0.5 indicates coils under theta (θ) conditions; lower valuestypically seen with increasing branching (see, e.g., with propylene sulfide homo-34 and copolymers 35 )reflect increasing contraction and lower propensity to entanglement; this trend was also recorded for PLAs (Figure 4A), which confirms their progressively lower tendency to entangle.…”

Melt Memory Effects in Poly(butylene succinate) Studied by Differential Fast Scanning Calorimetry

“…This distribution of melting points also reflects a distribution of lamellar thickness in the sample provoked by SSA thermal fractionation. This technique has been very useful to characterize ethylene/alfa-olefin copolymers, polypropylenes, block copolymers and more recently, segmented thermoplastic polyurethanes, recycled polyolefin blends, copolyesters and polysulfide based copolymers [39][40][41][42][43][44].…”